Two of three missions to Mars were on their way to the Red Planet as 1996 drew to a close. Mars Global
Surveyor, a mission to map the planet from orbit using some of the same instruments flown on the lost
Mars Observer craft, was launched successfully from Cape Canaveral by a Delta II booster on November 7
and should arrive at Mars September 12, 1997.Mars-96, launched on November 16 from Baikonur Cosmodrome, Kazakhstan, unfortunately never left Earth orbit. After some initial confusion, most observers now believe the fourth stage of its Proton booster failed to reignite to push the spacecraft out of Earth orbit. Instead, following separation from the booster, the craft reentered in a matter of hours to crash in remote regions of Bolivia or Chile. The booster stage reentered the following day into the Pacific Ocean some 900 miles east of Easter Island. Several eyewitness reports from northern Chile of fireballs that appeared to be an object breaking up apparently confirm the demise of the Mars craft in South America. All its scientific instruments, including an orbiter, two penetrators, and two small landers, were lost, a sad result for the Russian-led international consortium of scientists who developed them.
Mars Pathfinder, carrying the tiny Sojourner rover vehicle, was also successfully launched on a Delta II from Cape Canaveral in the very early morning hours of December 4. Because it takes a more direct path to Mars, the craft will arrive nearly two months before Mars Global Surveyor. If all goes well with the unique landing sequence, Pathfinder will arrive at Ares Vallis on Mars on July 4, 1997, where it will image its surroundings and sample the chemical composition of rocks with the Sojourner rover.
Delta II booster lofts Mars Global Surveyor.
Mission engineers studying a solar array on Mars Global Surveyor that did not fully deploy during the spacecraft's first day in space have concluded it should not significantly impair Surveyor's ability to aerobrake into its mapping orbit, or affect its performance during the cruise and science portions of the mission.
The panel is one of two 11-foot (3.5-meter) wings that were unfolded shortly after launch November 7 and are used to power the spacecraft. Currently, the so-called -Y direction array is tilted 20.5 degrees away from its fully deployed and latched position.
"After extensive investigation with our industry partner, Lockheed Martin Astronautics, using a variety of computer-simulated models and engineering tests, we believe the tilted array poses no extreme threat to the mission," said Glenn Cunningham, MGS project manager at JPL. "We plan to carry out some activities in the next couple of months using the spacecraft's electrically driven solar array positioning actuators to try to gently manipulate the array so that it drops into place. Even if we are not able to fully deploy the array, we can orient it during aerobraking so that the panel will not be a significant problem."
Line drawing of Mars Global Surveyor showing the current position of the solar panel in its fully deployed position, including a blow-up that shows the area in which the broken deployment mechanism is located.
Diagnosis of the solar array position emerged from two weeks of spacecraft telemetry and Global Surveyor's perfect performance during the first trajectory maneuver on November 21 in which a 43-second burn changed the spacecraft's velocity by about 60 miles per hour (27 meters per second), just as expected. The burn was performed to move the spacecraft on a track more directly aimed toward Mars, since it was launched at a slight angle to prevent its Delta third-stage booster from following a trajectory that would collide with the planet.
Both the telemetry data and groundbased computer models indicate that a piece of metal called the "damper arm," which is part of the solar array deployment mechanism at the joint where the entire panel is attached to the spacecraft, probably broke during the panel's initial rotation and was trapped in the two- inch space between the shoulder joint and the edge of the solar panel, Cunningham said.
Engineers are working to develop a process to clear the obstruction by gently moving the solar panel. The damper arm connects the panel to a device called the "rate damper," which functions in much the same way as the hydraulic closer on a screen door acts to limit the speed at which the door closes. In this case, the rate damper was used to slow the motion of the solar panel as it unfolded from its stowed position.
Engineers have been reevaluating the aerobraking phase of the Global Surveyor mission, which begins in September 1997 after the spacecraft slows into an elongated orbit around the planet using its onboard rocket engine. The solar arrays are essential to the aerobraking technique and will be used to drag the spacecraft into its final, circular mapping orbit. First tested on the Magellan spacecraft at Venus, aerobraking allows the spacecraft to carry less fuel, instead using its atmospheric drag to gradually lower itself into the correct orbit around the planet.
"Since we launched early in our window of opportunity, we will not have to aerobrake as fast to reach the mapping orbit, and this reduces the amount of heating that the solar panels are exposed to," Cunningham said. "In the event that our efforts to latch the solar array properly in place are not successful, this reduced heating should allow us to tilt the array in such a way to prevent it from folding up and yet still provide enough useful aerobraking force." Additional analysis and testing will be performed over the next several months to verify this hypothesis.
Meanwhile, Mars Global Surveyor continues to perform very well with science instrument calibrations beginning by the last week of November. At the same time, the Mars Relay radio transmitter has been turned on for a post-launch checkout. Radio amateurs around the world are gearing up to participate in a radio tracking experiment in which they will become receiving stations for the low-power beacon signal transmitted by the Mars Relay radio system.
Mars Global Surveyor is traveling at a speed of about 74,000 miles per hour (119,000 kilometers per hour) with respect to the Sun.
Two Hubble Space Telescope images of Mars, taken about a month apart on September 18 and October 15, 1996, revealed a Texas-sized dust storm churning near the edge of the martian north polar cap. The polar storm is probably caused by large temperature differences between the polar ice and the dark regions to the south that are heated by the springtime Sun. Increased sunlight also causes the dry ice in the polar cap to sublime and shrink.
Mars is famous for large, planetwide dust storms. Smaller storms resembling the one seen here were observed in other regions by Viking orbiters in the late 1970s. However, this is the first time that such an event has been seen near the receding north polar cap. The images provide new insights into the behavior of localized dust storms on Mars, which are typically below the resolution of groundbased telescopes. This kind of planetary weather report will be useful in preparing for the landing of Mars Pathfinder in July 1997 and the arrival of Mars Global Surveyor orbiter in September 1997.
To help compare locations and sizes of features, map projections (right of each disk) are centered on the geographic north pole. Maps are oriented with 0 degrees longitude at the top and show meridians every 45 degrees of longitude (longitude increases clockwise); latitude circles are also shown for 40, 60, and 80 degrees north latitude. Color images (http://www.stsci.edu/pubinfo/Pictures.html) were assembled from separate exposures taken with the Wide Field Planetary Camera 2.
Photo Credit: Phil James, University of Toledo; Steve Lee, University of Colorado and NASA
Top (September 18): The notch in the white north polar cap is a 600-mile (1000 kilometer) long storm - nearly the width of Texas. The bright dust can also be seen over the dark surface surrounding the cap, where it is caught up in the martian jet stream and blown easterly. The white clouds at lower latitudes are mostly associated with major martian volcanos such as Olympus Mons. This image was taken when Mars was more than 186 million miles (300 million kilometers) from Earth, and the planet was smaller in angular size than Jupiter's Great Red Spot!
Bottom (October 15): Though the storm had dissipated by October, a distinctive comma-shaped feature can be seen curving across the ice cap. The shape is similar to cold fronts on Earth, which are associated with low-pressure systems. Nothing quite like this feature has been seen previously either in groundbased or spacecraft observation. The snow line marking the edge of the cap receded northward by approximately 120 miles (200 kilometers), while the distance to the Red Planet narrowed to 170 million miles (275 million kilometers).
Two small science probes will hitch a ride on NASA's 1998 Mars Surveyor Lander to touch down
on Mars in 1999. The microprobes will demonstrate innovative new technologies as part of the New
Millennium program. "A successful demonstration of the microprobe technologies will enable a wide
range of scientific activities that would not be affordable with conventional technologies," said Dr. John
McNamee, manager of the 1998 Mars Surveyor Lander and Orbiter project at the Jet Propulsion
Laboratory."In particular, scientific investigations which require a relatively large number of surface stations distributed over the surface of Mars, such as seismic or meteorology networks, will be made possible by the microprobe concept," McNamee said. "In addition, microprobe penetrators may be the most efficient and effective way of obtaining soil samples and measurements from below the sterilized martian surface."
As they test technology that could lead to a meteorological network to study the martian climate, the Mars microprobes will complement the Mars Volatile and Climate Surveyor science package carried by the 1998 Mars Surveyor Lander by demonstrating an advanced, rugged microlaser system for detecting subsurface water. Such data on polar subsurface water ice should help scientists better estimate the global abundance of water on Mars.
Future missions to the planet could use similar penetrators to search for subsurface ice and minerals that might have been hospitable to the development of some form of life on Mars.
The 1998 Mars Surveyor Lander will be launched in January 1999 and spend 11 months en route to the Red Planet. Just before it enters the martian atmosphere the microprobes, mounted on the spacecraft's cruise ring, will separate and plummet to the surface using a single-stage entry aeroshell system. Chosen for its simplicity, this aeroshell does not separate from the microprobes, as have traditional aeroshells on previous spacecraft, such as the Mars Pathfinder and the Viking landers.
The probes will plunge into the surface at an extremely high velocity of about 446 miles per hour (200 meters per second) to ensure maximum penetration of the martian terrain. They should impact the surface within 120 miles (200 kilometers) of the main Mars '98 lander, which is targeted for the icy south polar region.
On impact, the aeroshells will shatter and the microprobes will split into a forebody and aftbody. The forebody, which will be lodged one to six feet underground, will contain the primary electronics and instruments. The aftbody, connected to the forebody by an electrical cable, will stay close to the surface to collect meteorological data and deploy an antenna for relaying data to Earth.
The microprobes will weigh less than 4.5 pounds (2 kilograms) each and be designed to withstand both very low temperatures and high deceleration. Each integrated package will include a command and data system, a telecommunications system, a power system, and primary and secondary instruments. Nearly all electrical and mechanical designs will be new to space flight.
"In addition to a team of industrial partners that will help develop advanced technologies to be demonstrated during the mission, we have just selected Lockheed Martin Electro-Optical Systems as a primary industry partner to participate in the integration and test program for the microprobes," said Sarah Gavit, Mars microprobe flight leader at JPL.
Technologies proposed for demonstration on this second New Millennium flight include a lightweight, single-stage entry aeroshell; a miniature, programmable telecommunication subsystem; power microelectronics with mixed digital/analog integrated circuits; an ultra-low-temperature lithium battery; a microcontroller; and flexible interconnects for system cabling.
In situ instrument technologies for making direct measurements of the martian surface will include a water and soil sample experiment, a meteorological pressure sensor and temperature sensors for measuring the thermal properties of the martian soil.
"The Mars microprobe mission will help chart the course for NASA's vision of space science in the 21st century, a vision that incorporates the concept of 'network science' through the use of multiple planetary landers," said Kane Casani, manager of the New Millennium program. The probes will become the first technology to be validated in this new network approach to planetary science.
"Networks of spacecraft will address dynamic, complex systems," Casani said. "For example, a single lander can report on the weather at one spot on a planet, but a network of landers is needed to characterize the planet's dynamic climate. Similarly, a single seismometer will indicate if a quake has occurred on a planet, but a network of seismometers can measure the size of a planetary core. We need multiple spacecraft to go beyond our initial reconnaissance to completely characterize dynamic planetary systems the way we are able to do on Earth."